1. Field of the Invention
This invention relates to motor driven rewind devices for cameras, and more particularly to a motor driven rewind device for cameras wherein energization of an electric motor is initiated by a rewind actuation, and wherein this energized motor brings a rewind shaft into engagement with a spool shaft of the film patrone to effect a rewinding operation of the film.
2. Description of the Prior Art
In the past there has been proposed a wide variety of motor driven film rewind devices for camera. Particularly in recent years, there has been in wide use a mechanism wherein driving of the rewind shaft by the driving torque of the motor is initiated after the rewind shaft has been engaged with the pawls of the film patrone shaft through the rewind coupler. According to this method, driving does not occur until the rewind shaft of the motor driven rewind device engages the patrone pawls, and only when engaged is the rewind driving initiated. Therefore, the initiation of a rewinding operation takes a long ramping time. This constitutes a drawback in that the rewinding time cannot be shortened.
A method to overcome the above-described drawback has been proposed by the applicants of the present patent application in U.S. Pat. No. 4,306,794 of Dec. 22, 1981. In this device, the rewind shaft while being rotated in a direction in which the film is rewound is lifted upwards to engage with the patrone hub, whereby it is made possible to shorten the ramping time at the time when the rewinding is initiated. However, since this method involves lifting of the rewind shaft while simultaneously rotating it, when the rewind coupler connected to the rewind shaft is to engage with the film patrone hub, as the patrone hub is given a driving force in two directions, or both along and about the rotation axis at the same time, the device provided with an absorption mechanism which works only in the vertical direction of the rewind coupler, as described in the above-cited patent, produces a drawback in that an increase of the driving torque of the electric motor for the purpose of establishing the engagement of the two members without failure results in the blockage of the vertically operated absorbing mechanism due to the friction force exerted by the driving force in the rotative direction. Therefore, the engagement of the rewind coupler and the patrone hub is not established with high reliability. That is, such a rewind device cannot transmit the driving torque of the electric motor to the shaft of the film patrone with good efficiency, and the reliability of film rewind control cannot be improved.
In this connection, it should be explained that such a motor driven rewind device has to fulfill the following requirements to make the film rewind feasible. That is:
(a) So long as a film exposure is being performed, unintentional actuation should not initiate a film rewinding operation.
(b) As the filming ends, a simple manipulation should suffice to quickly initiate a rewinding operation.
(c) The rewinding operation should continue without the necessity for the operator's finger to remain on the rewind control member. (If necessary, an operator using two cameras at a time can, while rewinding one camera, perform a filming operation with the other camera).
(d) As the rewinding operation is terminated, a simple manipulation should suffice to return the camera to the winding mode.
However, the above-described conventional motor driven rewind device, in view of (a), lacks a lock mechanism, and, even with the provision of a lock mechanism, it is only after the sprocket release button is depressed by the right hand that the rewind control member can be operated, thus inhibiting the quick switching to the rewind mode in view of (b). Also, with regard to (c), the operator must continue depressing the rewind control member with his finger during the time when the film is being rewound. Even for (d), there is a need to manually return the control member to the initial position. Thus, the need for manageability gives rise to many problems which must be solved. In this respect, the conventional motor driven rewind device cannot accomplish the object of switching the camera to the film rewind mode with high accuracy and reliability, and there has been a strong demand for improvements.